The wrong side of the tracks: quantifying barrier effects of transport infrastructure on local accessibility

Abstract

Cities can be characterized as distributions of accessibility. Two elements in the urban fabric that influence this distribution of accessibility are motorways and railways. These are powerful connectors in urban traffic systems but can also create strong barriers on a local scale. Based on a literature review, the negative effects of these barriers – also called severance – on social inclusion, health, and access to workplaces are described. Furthermore, it is pointed out that barrier effects are determined by three elements: transport infrastructure, built environment and people’s wishes and needs. Two morphological indicators are presented with which some of the barrier effects identified in the literature review can be quantified. One indicator is related to proximity to facilities, measured by network distance. The other relates to accessible offer of facilities, measured as the number of facilities within a given metric radius from each residential address. The indicators are demonstrated in a case study in Gothenburg, Sweden, where a four-lane motorway and railway tracks form substantial restrictions on the urban development of a former harbor area in the center of the city. In the case study the consequences of placing the infrastructure in tunnels is assessed. The analyses show how the increases in proximity to facilities and in accessible offer of facilities are spatially distributed in non-linear patterns. These results demonstrate the importance of taking into account transport infrastructure, built environment and people’s wishes and needs when assessing barrier effects. The case study indicates the potential of the proposed indicators for inclusion in a method for the quantification of barrier effects.